In this section, we'll take a good look at Linux filesystems so that you're familiar with all the nitty-gritty details that an administrator needs to know. To begin, I'll introduce "block devices". The most famous block device is probably the one that represents the first IDE drive in a Linux system:

/dev/hda

If your system uses SCSI drives, then your first hard drive will be:

/dev/sda

The block devices above represent an abstract interface to the disk. User programs can use these block devices to interact with your disk without worrying about whether your drivers are IDE, SCSI or something else. The program can simply address the storage on the disk as a bunch of contiguous, randomly-accessible 512-byte blocks.